The present invention relates to a screen assembly and, more particularly, to an improvement in translucent or transmissive screen assembly for use with a projection type television system or as a display panels.
Generally, a translucent or transmissive screen assembly is widely used with a projection type color television system of which the optical system is shown in FIG. 1.
Referring to FIG. 1 which shows the principle of the optical system, the projection type color television system has three cathode ray tubes C.sub.1, C.sub.2 and C.sub.3 for projecting light beams of different primary colors which are normally red, green and blue, onto the transmissive screen S through lens assemblies L.sub.1, L.sub.2 and L.sub.3, respectively. Three different color light beams must, when they are projected onto the projection screen, be mixed with each other, without any aberration, to form a proper color picture. The picture so formed on the screen is viewed by the observers who are situated at the right-hand side of the screen, that is, at one side of the screen opposite to the side of the tubes.
The screen of the above described type generally includes, as shown in FIG. 2, a diffuser plate member P.sub.1 and a layer of lenticular member P.sub.2. The diffuser plate member P.sub.1 has at least one surface thereof mat-finished, so that the light beam passing through the diffuser plate member P.sub.1 presents such a characteristics as shown in a graph of FIG. 3, in which the axes of abscissa and ordinate represent the diffusing angle and the relative intensity of the light beam, respectively. As apparent from the graph, the light beam passing through the plate member P.sub.1 tend to be outwardly diffused at a great angle of diffusion relative to the direction of travel of such incoming light beam.
On the other hand, the lenticular lens member P.sub.2 has at least one surface thereof formed with a plurality of parallel grooves, so that the light beam passing through the lenticular lens member P.sub.2 presents such a characteristics as shown in a graph of FIG. 4 in which the axes of abscissa and ordinate represent the diffusing angle and the relative intensity of the light beam, respectively. As apparent from the graph, the light beam diffused by the lenticular lens member scatters mainly in one direction, such as a horizontal direction, and scarcely scatters in a vertical direction. In view of this, if the members P.sub.1 and P.sub.2 are combined, the result would be such that the diffused light beam transmitted through the projecting screen is directed mostly towards the surroundings of the screen where the observers are situated and not in directions upwards and downwards of the projecting screen.
According to the conventional screen assembly, the matted surface F.sub.1 as shown in FIG. 5, of the diffuser plate member P.sub.1 the grooved surface F.sub.2 of the lenticular lens member P.sub.2 are arranged to face a beam travelling in a direction as indicated by the arrow H, while these members P.sub.1 and P.sub.2 are bonded together with the opposite, rear surface R.sub.1 of the diffuser plate member P.sub.1 held in contact with the grooved surface F.sub.2, or with the opposite rear surface R.sub.2 held in contact with the matted face F.sub.1 as shown in FIG. 6.
However, according to such conventional screen assembly, it has been found that, the larger the conventional screen is, the more the brightness of the image projected on such screen, which hereinafter referred to as screen gain GS, tends to be reduced. Therefore, the conventional screen assembly has a drawback in that the light beam passing therethrough tends to be diffused outwards at a great angle of diffusion relative to the surface of the screen, far from being directed towards the observers.
One reason for such reduction in the screen gain GS in the conventional screen assembly is due to an undesirable contact between the two layers. In the case where the lenticulared or grooved surface F.sub.2 of the lenticular lens member P.sub.2 is bonded to the rear surface R.sub.1 of the diffuser plate member P.sub.1 as shown in FIG. 5, an adhesive material fills up the grooves when the members P.sub.1 and P.sub.2 are clamped together during the manufacture of the screen assembly. Such adhesive material filling up the grooves constitutes a cause of light reflection at the boundary between the two layers and also reduction of the light transmissivity. Likewise, in the case where the matted surface F.sub.1 is bonded to the rear surface R.sub.2 of the lenticular lens member P.sub.2, the adhesive material applied therebetween may undesirably fill up interstices in the matted surface, thus resulting in similar disadvantages.